1. Field of the Invention
The present invention relates to immersion oils for use in microscopy and specifically relates to an immersion oil system in which the amount of a limited number of basic components may be varied in proportion to each other to create a wide variety of specific oils possessing one or more predetermined physical properties which may be required in a given microscopal application.
The image viewed in a microscope results from light rays, either reflected from or transmitted through the object or specimen to be viewed and then through the optical system of the microscope to the eye or other image sensing or recording devices. The optical system typically comprises the medium in which the object to be viewed is placed, a coverglass, the ambient atmosphere and the glass, plastic or other material which comprises the lens system of the microscope.
It is preferred to eliminate air gaps along a microscopal path of light for several reasons. Relative to glass, plastic, and immersion fluids typically used in the optical systems of microscopes, air or some other low refractive index material limits the angle of light that can enter the objective lens of the microscope, and hence limits the effective aperture and resolving power of the microscope. Replacement of such air gaps with a relatively high refractive index immersion oil thereby effectively increases the effective aperture and resolving power of the system.
Furthermore when light rays pass through one medium to another a certain amount of light is lost due to reflection which occurs at the interface of two different media. The degree of reflection varies with the degree of difference between the indices of refraction of the media through which the light rays pass. Inasmuch as the greatest differences in indices of refraction will typically occur between air (refractive index 1.00) and other light transmissive media (refractive indices typically ranging from about 1.48 to 1.60), it is ideally preferred to compensate for any air gaps which occur between the viewed object and the image sensing or recording device with a medium which is capable of maintaining a substantially uniform index of refraction with all of the other media through which the light will pass.
2. Description of the Prior Art
Immersion oils having predetermined indices of refraction are typically used to fill such air gaps. In addition to having an appropriate index of refraction, an immersion oil may also be required to have specific light absorption, fluoresence, and viscosity properties, depending upon the specific application to which the oil is to be put.
An immersion oil for use in general microscopy as specified by the standards of DIN .sctn.5884 should have a principal index of refraction (n.sub.e) of 1.518.+-.0.0004 and a principal dispersion factor (V.sub.e) of 44.+-.5. The standards of DIN .sctn.5884 further require that an immersion oil should not selectively absorb light having a wavelength in the range extending between about 380 and about 780 nanometers (nm). The standards also require that in normal illumination, an immersion oil should not visibly fluoresce. With respect to viscosity, an immersion oil complying with the standards must also be capable of maintaining the interface between the cover glass and the microscope objective, as well as between the condenser and the microscope slides. In addition the immersion oil must be physically and chemically stable.
Conventional immersion oils typically contain polychlorinated biphenyls (PCBs) which when blended with mineral oil and viscosity adjusting compounds provide a generally useful immersion oil having many of the ideal characteristics described hereinabove. In recent years, however, PCB's have been discovered to be carcinogenic, a hazard to the human environment, and are generally regarded as toxic. Furthermore PCB's are difficult to dispose of after use since they are extremely stable and nonbiodegradable.